What Should be Paid Attention to Before Buying and Deploying an SFP+ Direct Attach Cable (DAC)

With high-speed development and widespread use of generic cabling systems, fiber cables are widely applied in large and medium-sized networks as a high-bandwidth and safe data transmission medium. However, as the high cost of fiber cabling solutions, Direct Attach Cable (DAC) with copper transmission medium still plays an important role in network cabling systems.

What’s SFP+ DAC Cable?

SFP+ DAC (Direct Attach Cable) is also known as SFP+ Twinax copper cable. As its name implies, it takes copper cable as a material, so SFP+ DACs have the advantages of copper cable,  high electrical conductivity,  convenient installation, and cost-effectivity. 

SFP+ DAC has SFP+ form factor modules at either end of the Twinax copper cable that allows 10G network communication between switches and servers, but the modules are different from SFP+ optical transceiver. The SFP+ module connectors on SFP+ DAC don’t have an expensive laser and electronic component, which results in SFP+ DAC as a cost-saving and low consumption alternative solution of SFP+ optical transceivers. Besides, the transmission distance of SFP+ DAC is fixed, which depends on the length of the copper cable between the two ends of SFP+ connectors.

SFP+ Twinax copper cable is designed with very short distance transmission. The typical application scenarios are within racks and across adjacent racks, such as interconnected with top-of-rack switches and servers.

Attention Points of Buying and Deploying SFP+ DAC

Confirm the Compatibility of SFP+ DAC

The price of SFP+ copper cables is generally high offered by the original equipment manufacturers (OEM) and brands, so many communication service providers favored the third-party manufactures which are able to provide the industry-standard compliant SFP+ DAC. When choosing a third-party supplier, compatibility is the first priority that should be paid attention to. 

Then how to assure compatibility from a variety of third-party suppliers? First, you’d better choose the seller who is able to provide professional technical support and tell them your device brand and model number. Then confirm with them if their SFP+ DACs have been tested on your brand devices. It would be better if they could provide a test report. 

QSFPTEK is recommended, as far as we know, QSFPTEK provides timely technical support and their SFP+ direct attach cables are tested strictly before leaving the factory, testing reports are also available.

Passive or Active SFP+ DACs, Which to Choose?

The difference between active DAC and passive DAC is the active DAC structures with signal processing circuitry while the passive doesn’t, so active SFP+ DAC is much more expensive than passive SFP+ DAC. From the perspective of cost and power consumption, 

it is recommended to choose passive DAC within 7m transmission distances, and choose active DAC beyond 7m transmission links.


Calculating the SFP+ DAC Length You Need

For example, when you deploy SFP+ DAC cables in an 84 inch, 45 RU rack, it is estimated that the cable length is about 7 feet (2.1m) from the top of the rack to the bottom, and about 1.5 feet (0.45m) between adjacent ports. If there are 2 Top-of-Rack (ToR) switches and 20 2U SFP+  interface servers, the SFP+ DAC cable length needed approximately is 3m (2.1+2×0.45≈3m). Consequently, the cable length of the SFP+ DAC you need to buy is 3m.

Calculating the SFP+ DAC Length

Pay Attention to the Minimum Bend Radius

To ensure stability and extend the life of the SFP+ DAC cable, the actual bend radius when deploying should be greater than the required standard of SFP+ DAC minimum bend radius. The minimum bend radius is varied with the different wire gauges, as shown in the following table.

Wire Gauges(AWG)

Minimum Bend Radius


1.5 inch (38mm)


1.3 inch (33mm)


1.0 inch (25mm)


0.9 inch (23mm)


The above has explained the notices when buying and deploying SFP+ DAC cables from the aspects of compatibility, length, minimum bend radius, etc. I would love it if it is helpful to you. If you still have confusion about the SFP+ Twinax copper cable or any communication optics like transceivers and AOCs, you are welcome to consult the professional QSFTEK technical team via sales@qsfptek.com. QSFPTEK provides quality and compatible assured DAC cables at the best price.


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